Measure time until an std::future object becomes available

I am trying to measure the duration of an API call which returns an std::future object.

My current approach looks like this:

std::chrono::high_resolution_clock::time_point endTime, startTime = std::chrono::high_resolution_clock::now();

std::shared_future<API::response> responseFuture = API::request();

std::future_status status = responseFuture.wait_for(3s); // Some Timeout

if (status == std::future_status::ready)
  endTime = std::chrono::high_resolution_clock::now();
else
  // error handling

However, I'm unsure about the use of std::future::wait_for. cppreference.com states:

This function may block for longer than timeout_duration due to scheduling or resource contention delays.

I am not worried about blocking longer than timeout_duration, but I do require wait_for to immediately return once the std::future object is available, i.e. not having an implementation along the lines of

while(!ready){
  std::this_thread::sleep_for(10ms);
}

Is this guaranteed?